[jcranmer]

The tech here is P-wave detection. P-waves are somewhere around twice as fast as S-waves, so if you're 100-200km away from the hypocenter, it gives you that much advanced warning. Powerful earthquakes are still destructive at that range.

[Terribledactyl]

The other advantage is that once the seismic wave is detected, you can transmit that info at lightspeed vs the 10s of km/h that seismic waves propagate.